1. Field of the Art
This invention relates to a polarizing device with a high degree of planeness, cross dichroic prism and liquid crystal projector applying the polarizing device, and a method for fabricating the polarizing device.
2. Prior Art
There are liquid crystal projectors which employ a liquid crystal display device (an image sensor) for the purpose of projecting a picture image on a screen by way of the liquid crystal display device. Liquid crystal projectors, which are capable of projecting still picture images or movies on a large screen, are in wide use for presentation purposes or in home theaters. In a liquid crystal projector, a liquid crystal display device plays a role of image modulation in producing a picture image to be projected. Liquid crystal projectors which are capable of projecting color images on a screen can be categorized into two types, i.e., a three-panel type projector employing three liquid crystal display devices and a single-panel type projector employing a single liquid crystal display device. Lately, particularly three-panel type liquid crystal projectors are in general use because of high resolution of projected picture images.
In the case of a three-panel type liquid crystal projector, while light from a light source is separated into blue, green and red light components by color separation using dichroic mirrors and dichroic prism. The respective color components are modulated by the use of a liquid crystal display panel, and resulting image light of the respective color components are synthesized into a color image by the use of a dichroic mirror and a dichroic prism and projected on a screen by a projection lens.
A polarizing plate is located in light paths to and from a liquid crystal display device for the purpose of matching the direction of polarization of input and output light. By a polarizing plate on an input side, light rays of each color incident on a liquid crystal display device is attuned to linearly polarized light vibrating in the plane of polarization of either p- or s-polarization light, and modulated with picture signals of a corresponding wave range, rotating the plane of polarization. Of light rays of each color component which have been transmitted through the liquid crystal displace device, light rays polarized light in a specific direction of polarization alone are transmitted through the polarizing plate which is located on the output side, and the resulting image light of the respective color components are synthesized into a color image by means of a dichroic mirror and a dichroic prism.
Thus, polarizing plates are essential component parts for a liquid crystal projector, and optical accuracy of polarizing plates has a great influence on a picture image to be projected. That is to say, it is important for a liquid crystal projector to employ polarizing plates which are accurate in optical performance quality. Nevertheless, polarizing plates which are made of a synthetic resin film are soft by nature and difficult to maintain a high degree of planeness. In Japanese Laid-Open Patent Application 2000-352615, attempts are made to improve picture quality by solving the problem of irregularities in contrast as caused by polarizing plates. More particularly, in Japanese Laid-Open Patent Application 2000-352615, in order to solve the problem of degradations in contrast attributable to distortions of a synthetic resin film, a polarizing plate is bonded on glass which is small in absolute value of mean linear expansion coefficient
As mentioned above, a polarizing plate is made of an inherently soft synthetic resin film. A polarizing film with a polarizing function is bonded with a protective film, so that a resulting polarizing plate is soft as a whole. In Japanese Laid-Open Patent Application 2000-352615 mentioned above, by the use of a tackiness agent, a soft polarizing plate is bonded to a glass member like a prism which is high in rigidity. However, the tack strength of the tackiness agent is not strong enough for perfectly smoothing the surface of a bonded polarizing plate to a high degree of planeness, and more or less undulations remain on the surface, resulting in a polarizing plate which is inferior in surface planeness suffering from problems such as low accuracy in focusing picture images on a screen and low quality of projected picture images.